Peterbilt Tach Problem

[RobNJ]

I have a 2003 Peterbilt single axle dump. Model 330 CAT 3126 275hp Eaton 8 LL 29,000 miles. I'm having problems with the tach not working/working intermittently. Bought the truck used and the gauge was fine... after a while it started to crap out. The tach will not read at idle... . dead 0. If I hit the throttle substantially almost to the floor in neutral the tach will jump up. This happens when I'm driving to... right before a up shift. . ( in any ) gear in the upper rpm range the needle will jump up. . after the shift reads 0 again. Now heres the thing... sometimes... not always... after the truck has sat for a day or two I'll start it up and the tach will work fine... read idle/sweep through rpms fine... until i shut the truck off. Brought it to my mechanic who I trust, he took a quick look at it said it was getting a good signal maybe it's a bad tach head. Got a new tach head from Pete... . calibrated it for the truck... put it in... works the same as the old one



Any Pete or CAT guys out there come across this? Shed some light?

Bad sensor somewhere? bad ECU? Kinda want to save a little and not take it to Peterbilt unless I have to.



Any insight would be greatly appreciated. Thanks !

 

[DBoggs]

I'm not really familiar with the 3126 but I've owned a 3406E and currently hace a C15. There could be two possible places that the sensor picks up signal. Either on the bellhousing or on the gear housing on the front of the engine. The one on the gear housing usually isn't adjustable, it's a cam sensor and all you can do is replace it. The one on the bellhousing, if your truck has it, can usually be adjusted.



To adjust it loosen the jam nut and turn the sensor until it contacts the flywheel, then back it out 1/4 to 1/2 turn. Tighten the jam nut. Thats it. If that doesn't work the sensor may be bad.



Duane

 

[RobNJ]

Duane, thanks for the reply. I'm pretty sure its on the gear housing. Which is terrific cause the only way to get to it is to take the compressor off Anyway I'll look into it. In your opinion would the sensor cause it to work erratically like that?



By the way how do you like the 6. 7 ?

 

[DBoggs]

Yes it can cause that kind of erratic operation, I've had it happen before on 2 different trucks. All it is is a hall effect sensor and if it is too far away from the tone ring it takes more rpm to pick up the signal. The sensor could also be failing. Or there could be something more complicated but I always try the simple stuff first.



I love my 6. 7, so far it has been 100 percent trouble free. I have about 4500 miles on it.



Duane